Two known low voltage lighting systems are illustrated in FIGS. 1 and 2. Such systems generally are supplied with operating power by a conventional house current circuit supplying about 120 volts AC. However, power is distributed to individual loads at a reduced voltage, for example, 12 volts AC.
The prior art system of FIG. 1 receives input power at 120 volts AC 101. The stepdown transformer 103 receives the input power on its primary side 103a and produces a low voltage output, such as a 12 volt AC output, on its secondary side 103b. Power at 12 volts AC is distributed to loads 105a-105d by parallel wires 107a and 107b. The described prior system suffers a disadvantage in that a lamp load which is electrically remote from stepdown transformer 103 (for example, lamp load 105d) will burn more dimly than an identical lamp load electrically close to stepdown transformer 103 (for example, lamp load 105a). This results from the resistive loss and consequent voltage drop (V.sub.d) which occurs in wires 107a and 107b, as explained below.
A lamp intended to dissipate a particular power at a nigh voltage draws a lower current than a similar lamp designed to operate at the same power, but at a lower voltage. The relationship between power (P), voltage (V) and current (I) known as Watt's Law is: P=VI. But the voltage drop in the wires obeys Ohm's Law: V.sub.d =IR, where R is the resistance of the wire. The problem of voltage drop is exacerbated in such low voltage systems, because in accordance with Watt's Law, the current drawn through the wires in a low voltage system output.
One solution to the problem discussed above is to distribute power at the high voltage, but locally reduce the voltage for each lamp, as illustrated in FIG. 2. In such a system, power is supplied at 120 volts AC 101 and distributed in parallel wires 201a and 201b. Each lamp load 105a-105d is associated with a corresponding local stepdown transformer 203a-203d. Although this conventional system significantly reduces the problem of a voltage drop in wires 201a and 20lb, by significantly reducing the required current flow through those wires, it does so at the expense of requiring a stepdown transformer for each lamp load. Furthermore, although the voltage drop problem is greatly reduced, it is not eliminated.
Finally, low voltage systems such as described above are frequently configured to be flexible in the number and positioning of lamp loads with respect to distance along power distribution wires 107a and 107b or 201a and 201b. However, by changing the number of lamp loads present in the system, the total voltage drop is varied, resulting in an overall brightness change in the remaining lamp loads. This variation in brightness is another undesirable feature of systems of the prior art.
Therefore, it is desired to provide a system wherein a uniform, fixed voltage is provided at each lamp load. Such a system has been achieved by means of the present invention, whose principal aspects are now described.